Based on earlier findings suggesting that excessve alcohol consumption can initiate formation of a unique form of hemoglobin having properties similar to those of the known minor hemoglobins, the size of the minor hemoglobin fraction (hemoglobin A1 fraction) was determined in 43 normoglycemic alcoholic patients and 41 healthy volunteers. In the alcoholic patients the mean value of the fraction was significantly higher (P less than 0.0001) than in the normal subjects. In patients with values greater than 3 s.d. above the normal mean, serum hepatic enzyme activities, although elevated in most cases, were normal in some, indicating that the proportion of hemoglobin A1 was unrelated to liver function. The hemoglobin A1 fraction increased in alcoholic individuals who continued to drink heavily and declined at the rate of erythrocyte turnover in an alcoholic patient who stopped drinking. Chemical evidence obtained thus far strongly suggests that erythrocytes from alcoholic individuals contain a hitherto unrecognized form of hemoglobin A1. Evaluation of the hemoglobin A1 fraction is a simple and relatively rapid procedure for screening for excessive alcohol consumption.